The present invention relates to sulfur foams.
A recent patent issued to Dale and Ludwig, U.S. Pat. No. 3,337,355, discloses the production of a sulfur foam using the following steps:
(a) heating sulfur to above its melting point;
(b) blending a stabilizing agent with the molten sulfur;
(c) blending a viscosity increaser with the molten sulfur, steps (b) and (c) being taken in either order with respect to the other;
(d) forming bubbles in the molten sulfur, and
(e) cooling the molten sulfur to below its melting point.
My commonly assigned patent application Ser. No. 344,694, discloses the preparation of sulfur foams using sulfur plus an aromatic composition such as phenol plus an acid and a polyisocyanate. My commonly assigned application Ser. No. 438,508 discloses preparation of a sulfur foam using sulfur plus an acid plus a polyisocyanate; the sulfur can be plasticized, if desired, for example using an aliphatic compound.
Proceedings, National Academy of Sciences, U.S.A., 46, 822 (1960) and Jo. Chem. Eng. Data 8, No. 4, 620 (Oct. 1963) disclose that maleic anhydride and some other anhydrides are sensitive to decomposition and will liberate a gas upon exposure to a base at a temperature above about 90.degree. C. See also Quarterly Reports on Sulfur Chemistry, 5, No. 3, 212 (1970)--Fourth Organic Sulfur Symposium, Venice, Italy, which discloses the reaction of sulfur with maleic anhydride to give a black polymer with H.sub.2 S evolution.